It is common to provide magnetic tape write/read head assemblies having one or more write/read transducer elements positioned transverse to the intended path of a magnetic recording medium, e.g., tape, for writing data on and reading data from parallel tracks on the tape. It is also known to include servo information on at least some of the tracks and provide servo transducer elements on the recording/playback head for reading such information to enable control of the lateral position of the head assembly, thereby dynamically maintaining the respective transducer elements of the head assembly relative to tape tracks. With the use of servo control, data track widths can be made significantly narrower and the data capacity of the recording medium can therefore be increased.
Various techniques for providing servo tracks have been previously employed. For example, it is known to provide dedicated servo tracks on the medium at the time of manufacture. However, it is often desirable to enable an end user to write a servo pattern on the medium in the field as opposed to factory writing of servo information. This allows the end user to add the servo information to either a blank medium or utilize a medium which was either intentionally or unintentionally erased.
There are a substantial number of different servo track configurations for providing servo control. For example, one continuous track following single frequency system and servo track configuration is generally characterized by the utilization of erased and non-erased portions in a servo carrier band to provide servo tracks for servo control as described in U.S. Pat. No. 5,229,895 to Schwarz et al., entitled "Multi-Track Servo Recording Head Assembly." As described therein, a write element is used to write a servo carrier signal extending substantially uniformly over a dedicated servo section along a length of the tape followed by erasing various portions of the written servo section to define one or more servo track pairs along the length of the tape. One or more servo read elements may be used to read servo information from the servo tracks for generation of a position signal for control of the head assembly position relative to the tape.
Another continuous track following single frequency system and servo track configuration is generally characterized by the utilization of noncontiguous servo tracks, i.e., separated servo tracks of single frequency, in an erased servo section as described in U.S. Pat. No. 5,262,908 to Iwamatsu et al., entitled "Tracking Control Device For Magnetic Recording/Reproducing Apparatus" (particularly, FIG. 4A). As described therein, the servo information is read from a servo track by at least one pair of servo read heads, e.g., a position signal is generated from the position of the servo read heads relative to the servo track.
However, the different single frequency systems and servo track configurations have ambiguity associated with identifying which servo track is being used for deriving the position signal to provide for servo control of the system. In other words, a track following magnetic head assembly using these single frequency servo systems cannot distinguish between servo tracks being read. For example, when servo track pairs are defined such as by erased and non-erased portions, the system cannot distinguish which servo track pair is being read. Although the servo track provides adequate positioning information, it does not provide information as to which servo track the servo head is currently utilizing to generate the position signal for servo control. Therefore, if the servo head is unintentionally repositioned, a misidentification of the servo track being used for servo positioning of the data read/write elements occurs. Such unintentional head displacement is exacerbated as advanced tape drives utilize decreased track widths and decreased track pitch.
Various systems include techniques for attaining some improvement with respect to the ambiguity in servo track identification. For example, sophisticated software algorithms for identifying which servo track is being read have been used. Such algorithms generally provide for identification by repositioning the head below or above a servo track group and counting servo track crossings to reach the proper servo track. Other methods, for example, use a gross position transducer, external to the head, such as an optical line counter or read information recorded on data tracks to confirm servo track position.
Further, additional techniques such as writing servo track identification frames at the beginning of tape (BOT) and end of tape (EOT) in order to identify the correct servo track when the magnetic head loses servo lock in the case of, for example, a sudden head displacement, have also been used. In such a servo configuration, the drive must undesirably return to the BOT or EOT to read the identification frames and thereby determine accurate servo track position, i.e., servo track identification.
In addition, other systems, using servo track configurations including distinguishable servo tracks, i.e., such as servo tracks provided by writing adjacent tracks at different frequencies, have been used to alleviate ambiguity with respect to servo track identification. However, such configurations have the disadvantage of increasing the cost of the servo head and read circuit electronics because of the different frequencies utilized. Such system configurations also have the increased difficulty of producing a servo write head with different carrier frequencies for adjacent tracks while maintaining the necessary track pitch and track widths. For precision writing, this typically requires that the pattern be written in the factory.
Furthermore, in addition to problems of ambiguity with respect to the identification of servo tracks, it is desirable to know other information regarding the tape data cartridge or tape of the cartridge as the tape is being accessed. For example, it is desirable to know longitudinal tape locations when searching at high speed without slowing the drive down to read the actual data and format signals while simultaneously using sophisticated software algorithms to keep track of servo track locations. In a typical data cartridge system, longitudinal tape locations may be approximated by timing at a known speed, or by periodically reading header information in recorded data tracks and calculating longitudinal tape locations. This limits the accuracy and speed of such systems in determining particular locations on the tape.
For the above reasons and other reasons that will be apparent from the description below, alternatives to the configurations such as those described above are needed to overcome difficulties associated therewith. For example, the identification of servo tracks is desired. Further, it is desirable to provide information regarding various tape characteristics, for example, tape locations, BOT indicators, load indicators, etc.